1. Field of the Invention
The present invention relates to a magnetic tape recording/reproducing apparatus.
2. Description of the Prior Art
As a helical scanning magnetic recording/reproducing apparatus (as will be shortly referred to as the "VTR") using a magnetic tape having a width if a half inch, there is generally known in the prior art the VHS system (one of the industry standard formats) or the S-VHS system (another industry standard format), which uses a rotary drum D, as shown in FIG. 1.
In these VTR systems, video heads SP1 and SP2 having different azimuth angles of .+-.6 degrees each ether for standard (tape speed) recording and playback abbreviated "SP" mode, video heads EP1 and EP2 having different azimuth angles of .+-.6 degrees each ether for extended recording and playback (typically 1/3 of the standard tape speed standardized in the VHS system for obtaining an extended recording and playback time for a given length of tape, often abbreviated "EP" mode), an, audio heads A1 and A2 having different azimuth angles of .+-.30 degrees are arranged at spacings of predetermined angles around the rotary drum D. Moreover, the audio signals inputted to the VTR have their frequencies modulated to produce recording audio signals, which are sequentially recorded in the deeper portion of the magnetic layer of a magnetic tape T by the actions of the audio heads A1 and A2 while preceding the video heads EP1 and EP2 or SP1 and SP2 in the operations. Of the luminance signals and chroma signals separated from video signals inputted to the VTR, on the other hand, the former luminance signals are subjected to an FM modulation to produce the modulated luminance signals, and the latter chroma signals have their frequencies converted down to produce the down-converted (frequency) chroma signals. Both of the modulated luminance signals and the down-converted chroma signals have their frequencies multiplexed to produce the recording video signals. These video signals are recorded in the upper portion over the deeper portion of the magnetic layer of the magnetic tape T by the actions of the video heads EP1 and EP2 or SP1 and SP2 while being superposed over the audio signals by the aforementioned audio heads A1 and A2.
According to the standard (i.e., one of the industry standards) of the VHS system, the audio heads A1 and A2, the video heads EP1 and EP2 and the video heads SP1 and SP2 should satisfy at least the following conditions:
(1) The recording time difference between the video signals and the audio signals to be recorded in the same portion on the same track should be such that the audio signals are recorded in the standard play mode while preceding the video signals by 0 to 2 fields, and those magnetic heads have their azimuth angles in the opposite directions; PA1 (2) The recording time difference between the video signals and the audio signals to be recorded in the same portion on the same track should be such that the audio signals are recorded in the extended play mode while preceding the video signals by 4/3 to 10/3 fields, and those magnetic heads have their azimuth angles in the same directions; PA1 (3) In the standard play mode, the relation between the video track and the audio track to be recorded in the same portion of the same track should be such that the distance to the upper or lower end of the audio track is no less than 10 .mu.m and no more than 29 .mu.m with respect to the video track center; and PA1 (4) In the extended play mode, the relation between the video track and the audio track to be recorded in the same portion of the same track should be such that the audio track width is no less than 16 .mu.m and no more than 19.3 .mu.m from the upper end of the video track.
In the VTR of the VHS system satisfying those conditions (1) to (4), the video signals and the audio signals are commonly recorded/reproduced in one track. In order to after-record the audio signals and to enhance the quality of the video signals, a magnetic recording/reproducing method for recording/reproducing the three tracks as one set, is proposed in Japanese Patent Laid-Open No. 47292/1987 by the same applicant.
The aforementioned VTR capable of recording/reproducing the VHS system of the prior art and a set of three tracks has to be equipped with, in addition to the intrinsic three sets of magnetic heads for the VHS system of the prior art, other three sets of magnetic heads for recording/reproducing the three tracks as one set.
According to the prior art, however, it is difficult space-wise and undesirable for the complicated structure to arrange all those magnetic heads over the rotary drum.